Electric furnace



Sept. 23, 1941. DREYFUS ELECTRIC FURNACE Filed Sept. 28, 1939 //1 vewf'or Ludwzlg 17ml us 06)" WHO/ 11 Patented Sept. 23, 1941 ELECTRIC FURNACE Ludwig Dreyfus, Vasteras, Sweden,

Svenska Elektriska Allmiinna Vasteras, Sweden,

Application September 28, In Sweden Oct 2 Claims.

In all metallurgical furnaces, a stirring of the bath is necessary for temperature equalisation, acceleration of the reactions and in alloy mixing furnaces for mixing the bath in order to achieve an even product. In furnaces, in which the heat is transmitted to the bath through its surface, for instance in arc furnaces, the stirring action also is necessary in order to avoid an overheating of the part of the charge below the electrodes.

Generally a stirring by hand is used, but for special processes a manual stirring has proved to be insufiicient.

The present invention has for its object an arrangement, by which a strong stirring of the bath can be obtained by electromagnetic forces with very low frequencies, for example 1-8 periods per second. According to the invention, a polyphase fiat winding is located in the bottom of the furnace below the lining, but inside the iron mantle of the furnace. In order that the induction lines from the winding shall penetrate the charge in spite of the comparatively thick lining of the bottom, the winding preferably is so formed that it covers almost the whole bottom. The winding further preferably is made as a two phase winding with one phase of the winding consisting of a central placed fiat circular coil, whereas the other phase of the winding is divided into two semicircular coils arranged symmetrically to and close above or below the former.

On the accompanying drawing, one form of the invention is shown in a vertical section in Fig. 1; Fig. 2 shows the invention in plan view, and Fig. 3 shows schematically the windings in the bottom of the furnace and the generator for the low frequency current.

In Fig. 1, I designates the lower part of the furnace and 2 the bath. The heating is supposed to be achieved by means of arc electrodes l6 shown schematically at Figs. 1 and 2. The winding, which is placed in the bottom of the furnace, is arranged as indicated by Fig. 2 and consists of a circular coil 3 arranged symmetrically around the vertical axis of the furnace, which coil carries the current of one phase, and two semicircular coils 4 and 5 symmetrically arranged below this coil 3, which coils 4 and 5 carry the current of the other phase. The direction of the currents is indicated by the arrows. The chief advantage with this symmetrical arrangement is that there is no mutual inductance between the phases. Each winding contains suitably only one layer of conductors.

assignor to Aktlebolaget,

a corporation of Sweden 1939, Serial No. 296,911 ober 3, 1938 In the left half of Fig. l, the induction lines are shown, which are generated in the charge by the current in the coil 3 if the counter-magnetizing action of the eddy currents in the bath can be neglected, and in the right half of the figure the induction lines from the other phase are shown. In fact, it is intended to generate so large eddy currents that the penetration of the induction lines is smaller, which with the common dimensions of large arc furnaces will be the case already at a frequency of about one per second. At this frequency, the bottom of the iron vessel may serve as a yoke 6 for the return of the induction lines outside the winding.

It is suitable to dimension the different phase windings, so that the maximum induction in the yoke will be about the same for the two phases, because then the yoke is utilized in the most favorable manner. With the shown arrangement of the winding with one coil in one phase and two coils in the other, there will be a considerable difference between the kva. consumed in the two phases, but at the low frequency in question the currents of the two phases suitably are generated in two separate commutator generators, so that the difference in power will be of very little importance.

The dotted curves 1 in Fig. 2 show the horizontal streams achieved in the charge, and in Fig. 3 the windings 3, 4, and 5 are shown with the windings 4 and 5 above instead of beneath the winding 3; and 8 and 9 are the armatures of the commutator generators delivering the low frequency current. The field windings of these generators are shown at I0 and II respective-- ly, and I2 and I3 are regulable resistances for regulating the excitation current of the generators, which current is delivered from an alternating current source not shown on the drawing.

The two commutator generators are arranged on a common shaft l5 and are driven by a motor I4.

I claim as my invention:

1. A metallurgical furnace with heat supply at the free surface of the bath, comprising an iron vessel, a lining inside said vessel, a twophase winding between the lining and the bottom of the iron vessel, said winding consisting of a flat circular coil belonging to one phase and two flat semicircular coils belonging to the other phase, the latter coils being arranged in one plane and symmetrical to and close to the said circular coil, and a two-phase source of alternating current of below 10 periods per second feeding said winding.

symmetrical to and close to the said circular coil, the coils oi the diflerent phases being so dimensioned that they generate practically the same induction in the bottom of the vessel, and a 5 two-phase source of alternating current oi below 10 periods per second feeding said winding.

LUDWIG DREYFUS. 

